1. Field of the Invention
This invention concerns an improved process for preparing predominantly linear alcohols by the reaction of synthesis gas and terminal or internal olefins in the presence of a catalyst system.
2. Prior Art
The processes of hydroformylation and carbonylation are well known in the art and involve reactions represented by: ##STR1## wherein the aldehydes and alcohols produced generally correspond to the compounds obtained by the addition of a carbonyl or carbinol group to an olefinically unsaturated carbon atom in the starting material with simultaneous saturation of the olefin bond. Isomerization of the olefin bond may take place to varying degrees under certain conditions with consequent variation in the products obtained.
The hydroformylation reaction does not generally proceed in the absence of catalysts, and a disadvantage of many of the hydroformylation processes disclosed heretofore is their dependence upon the use of catalysts, particularly the commonly used cobalt-derived homogenous `oxo` catalysts, which generally necessitate the use of exceedingly high pressures to remain stable under the conditions employed. A further disadvantage of many of the processes disclosed heretofore is their inability to produce hydroformylation products comprising substantial amounts of alcohols, thereby necessitating a separate aldehyde hydrogenation step when alcohols are a desired product. The production of hydroformylation products having a relatively high normal to branched product isomer ratio is also often exceedingly difficult, if at all possible, in many of the practical scale processes now in use. Another problem in many commonly practiced hydroformylation processes is by-product formation on account of competing reactions. Examples of such unwanted by-products include alkanes, formed through competing olefin hydrogenation, olefin isomers formed through double bond isomerization, ketone formation and aldols generated as a result of product aldehyde condensation reactions.
In commercially practiced hydroformylation processes cobalt- and rhodium-catalyzed systems are most commonly used.sup.1, while cobalt and rhodium have been the focus of much of the prior hydroformylation research, numerous other metals have been disclosed as catalysts for this synthesis. FNT (.sup.1 For a review of the prior art pertaining to the use of cobalt and rhodium-based hydroformylation processes see: R. L. Pruett, "Advances in Organometallic Chemistry", Vol. 17, page 1 (1979).)
Typical of the prior art relating to the use of ruthenium as a hydroformylation catalyst are the publications of Wilkinson and co-workers. In British Pat. No. 1,138,601, Example 6, the hydroformylation of the alpha-olefins (1-hexene) to aldehydes is described using soluble, phosphine-stabilized ruthenium catalyst precursors, such as [(Ph.sub.2 EtP).sub.6 Ru.sub.2 Cl.sub.2 ]Cl. Here moderately high pressures are used and the use of a two step hydroformylation and subsequent hydrogenation step as a synthetic route to alcohols is discussed. Additional information regarding the use of a variety of tertiary-phosphine-ruthenium complexes in the catalytic hydroformylation of alkenes to aldehydes-particularly the dependence of conversion and aldehyde ratios upon catalyst concentration, temperature, partial and total pressures, nature of the substrate, and the addition of excess phosphine may be found in a second publication by this group in J. Chem. Soc., page 399 (1976). Similar classes of catalysts are disclosed also in U.S. Pat. No. 3,239,566, assigned to Shell Oil Company. In particular, this patent relates to the production of aldehydes and/or alcohols by the addition of carbon monoxide and hydrogen olefinic hydrocarbons in the presence of a catalyst consisting of a ruthenium or rhodium component in complex combination with carbon monoxide and a trialkylphosphine. Here, the greatest percentage of the converted olefins form alcohols and aldehydes with less than seven carbons.
The use of ruthenium salts, such as ruthenium(III) chloride and ruthenium stearate, as well as ruthenium carbonyls and ruthenium on carbon, as catalyst precursors for the hydroformylation of olefins to straight-chain and branched aldehydes is disclosed in British Pat. Nos. 966,461 and 999,461, assigned to Imperial Chemical Industries Limited. Pettit, in U.S. Pat. No. 4,306,084, describes an oxo process reaction where the ruthenium carbonyl catalyst is maintained in a basic solution. Recently the cluster anion, [HRu.sub.3 (CO).sub.11 ].sup.-, has been shown to catalyze the hydroformylation of ethylene and propylene to C.sub.3 -C.sub.4 aldehydes in dimethylformamide at 100.degree. C. (see C. Suss-Fink, J. Organomet. Chem., 193, C20 (1980)).
Polymer-bound ruthenium hydroformylation catalysts, prepared for example by reacting diphenylphosphinated styrene-divinylbenzene resins with phosphine-stabilized ruthenium carbonyls, have also been described recently. Pittman, in J. Org. Chem. 46, 1901 (1981), finds improved normal/branched aldehyde ratios with these resins compared with homogenous catalyst versions. The more desirable alcohol products are not reported to be formed with this class of ruthenium catalyst.
U.S. Pat. No. 3,239,569 discloses the production of aldehydes and alcohols in a single stage conversion which comprises contacting an olefinic hydrocarbon with carbon monoxide and hydrogen in the presence of a catalyst system comprising cobalt in complex combination with carbon monoxide and a trialkylphosphine. Here again, the majority of the hydroformylation products were six carbons or less.
There is then a need in the art for a one stage process for preparing alcohols from olefinically unsaturated compounds by a process which utilizes lower pressures and results in a high yield of predominantly linear alcohols of the C.sub.3 -C.sub.20 range.
An object of this invention, therefore, is to oxonate terminal and/or internal olefins, but particularly higher molecular weight, C.sub.7 -C.sub.14 linear alpha olefins fractions, at pressures lower than previously used, to produce predominantly aliphatic C.sub.8 -C.sub.15 range alcohols and to outline a method of recovering the product alcohol from the non-volatile, ruthenium-containing, amine promoted catalyst.
The advantages of this process include a yield with a high percentage of linearity of surfactant grade alcohols and intermediate aldehydes; ease of processing, because in many previous systems where cobalt is present one must "de-cobalt" the system; and, the feature of the low volatility of the system compared to a cobalt system.